Dissolved air flotation is one of several processes used to clean and purify water. The process may be used for removing suspended solids, including organisms, from fresh water for municipal water supplies, or for removing suspended solids from industrial wastewater. In the dissolved air flotation process, influent water is mixed with a coagulant to form flocculent particles, and then white water (air-saturated high-pressure water) is injected into a tank of the influent water/flocculent mixture to form air bubbles that attach to the flocculent particles and lift them to the surface. In some processes, the coagulant may be omitted, and suspended solids can be lifted by the air bubbles. The particles lifted to the surface accumulate in a layer of scum or sludge, referred to as the float. This layer is skimmed off the surface of the tank, while clean water is drawn out of the bottom of the tank.
In our prior U.S. Pat. Nos. 6,921,478, 7,767,080, and 7,033,495, we disclosed a dissolved air flotation system comprising a flocculation tank with an output communicating downstream to a flotation tank, and white water injection system for injection finely aerated water into the flotation tank, a skimmer for pushing float over the downstream end wall of the flotation tank and a conveyor belt for carrying off the float after it has been skimmed, and a clean water outlet at the bottom of the flotation tank.
Experience with the device described in our prior patents has led to various improvements.